Various membrane abnormalities of sickle RBC have been described. While it seems likely that some of these play an important role in sickle cell disease (SCD) pathophysiology, their etiology remains obscure. This application is divided into three interrelated projects. Project A examines RBC/endothelial interactions. Cultured human endothelium will be used to evaluate the possible influence of alpha-globin gene number, the possible role of fibrinogen/fibronectin in RBC-endothelium bridging, and the pharmacologic modulation of adherence by various agents. Tenacity of sickle RBC adherence to endothelium will be measured under flowing conditions in a flow channel apparatus. Alternative techniques will be developed to solve some of the problems inherent in the endothelial adherence assay. The role of RBC surface charge distribution will be re-examined, using electron microscopic visualization of RBC surface charge distribution after charge-labelling with cationized ferritin and colloidal iron. Project B examines RBC/macrophage interactions as a possible determinant of hemolytic rate in SCD. The role of sickle RBC membrane abnormalities (particularly the possible role of RBC-bound immunoglobulin) in abnormal interactions of sickle RBC with human macrophages will be examined. Project C examines the hypothesis that accelerated RBC autoxidation is responsible for development of sickle RBC membrane abnormalities. Spontaneous generation of oxygen radicals by normal and pathologic RBC will be directly measured, and the possible role of membrane-bound hemichrome in generation of hydroxyl radical by sickle RBC will be studied. Specific sickle RBC membrane abnormalities (calcium-ATPase deficiency, intra-molecular disulfide bonding, and lipid peroxidation) will be evaluated to determine the contribution of specific oxygen radicals to their development. The effect of these radicals upon normal RBC membranes will be identified. Radical-induced oxidation of normal RBC membranes will be studied to determine whether this process is responsible for abnormal interactions of sickle RBC with endothelium and macrophages (and perhaps, therefore, for the vasocclusive and hemolytic components of SCD). It is hoped that these studies will expand our understanding of the sickle RBC membrane and the role of membrane abnormalities in SCD pathophysiology. This should hasten the development of rational modes of therapy.